(a) Field of the Invention
The invention relates to a needle holder positioning structure for a safety syringe, more particularly to a low-cost structure that allows precise positioning.
(b) Description of the Prior Art
R.O.C. Patent Publication No. 332433 discloses an improved safety syringe structure having a needle holder positioning structure as shown in FIGS. 6 to 10. A rear end of a needle holder 5 is provided with a flared hole 51 which is enlarged to form an arrow-shaped cavity 52 for receiving an arrow-shaped coupling member 62 provided at the front end of a piston head 61 of a piston 6. After injection, the coupling member 62 and the cavity 52 are coupled integrally. Therefore, when the piston 6 is pulled back, the needle holder 5 together with the needle 53 is disengaged from the neck portion 71 of the syringe 7 to pull the needle 63 into the interior of the syringe body 72 of the syringe 7 so as not to expose on the outside to ensure safety.
Further, since in that patent the needle holder 5 is disposed in the neck portion 71 of the syringe 7, in order that the needle holder 5 can be smoothly pulled back, the needle holder 5 must be formed from elastic rubber material instead of the conventionally used plastic material. However, as rubber is much more expensive than plastic, and the elastic characteristic of rubber may affect the positioning of the needle 53, that patent has the disadvantages of high costs and improper positioning.
There are other related prior art patents, which include U.S. Pat. Nos. 4,932,939, 5,163,907, 5,910,130, 5,879,339, 5,902,277, 5,902,271, 5,902,270, 5,902,269, 5,395,346, 4,737,144, 5,344,403, and 5,569,203.
The primary object of the present invention is to provide a needle holder positioning structure for a safety syringe, which is inexpensive to manufacture.
Another object of the present invention is to provide a needle holder positioning structure for a safety syringe, which permits precise positioning of the needle.
In order to achieve the above objects, the present invention is characterized in that the inner edge of a lower end of a neck portion of a syringe is upwardly and integrally formed with a forked elastic sleeve and hook members, and a needle holder is corresponding provided with depressions so as to couple the needle holder to the neck portion of the syringe by means of hooking and elastic retention, and the needle holder together with the needle can be pulled back into the interior of the syringe. Furthermore, the needle holder can be made of plastic material. Plastic needle holders are low-cost and permit precise positioning as compared with rubber needle holders.